Method of readjusting the current supplying and supporting metal rods of continuous self-baking electrodes



July 5, 1949.

R. JOUANNET METHOD OF READJUSTING THE CURRENT SUPPLYING AND SUPPORTINGMETAL RODS OF' CONTINUOUS SELF-BAKING ELECTRODES Filed May 5, 1948 JZ18a,

INVENTOR.

vefl /cfua naaf Patented July 5, 1949 METHOD OF READJUSTING THE CURRENTSUPPLYING AND SUPPORTING METAL RODS OF CONTINUOUS SELF-BAKING ELECTRODESRobert Jouannet, La Pra assignor to Elektrokem Norway z, near Modane,France, ist A/ S, a corporation of Application May 5, 1948, Serial No.25,174

7 Claims.

The use of vertical studs or rods for support- I ing and supplyingelectric current to continuous electrodes has previously been suggestedin United States Patent No. 2,224,739 to Manfredini. The presentinvention relates to improvements upon the inventions of that earlierpatent.

In the operation of a continuous electrode such as is employed in theproduction of aluminum, the bottom portion of the electrode reaches atemperature above about '750 and on the surface approaches thetemperature of the bath or about 950 C. At the top, the electrode willhave a temperature inthe order of from 135 C. to 250 C. As the electrodeis consumed, additional quantities of electrode paste are added. Thispaste is made up of mixtures of carbonaceous material such as ground-upcoke and a binder of a bituminous nature. As is well known in this art,the binder ordinarily employed in making the paste has a melting pointabove normal temperature but substantially below the temperature of 135C. so that the so-called paste is substantially solid at normal`temperatures but readily melts at thev temperature near the top of theelectrode. the paste in a molten state until very gradually and over thecourse of many days the binder is volatilized suiilciently so that thenastyy mass rst becomes suliiciently solid not to ow and finally becomesthoroughly coked.

In the Manfredini structure, tapered rods eX- tend down from the topinto the mass. Manfredini recommends that these be arranged in threerows or tiers. The lowest may, at its low point, go down withinabout cm.of the' bottom of the electrode, the second is about 20 lcm. higher andthe third is again 20 cm. above the second. Thus when the lowest one isreinserted after being drawn out and cooled, it

will be about 80 cm. from the bottom of thel electrode. The internalresistance of the mass increases toward the top, and wherethe mass isfluid it has substantially no conductivity.

4Manfredini states that his second tier of rods carries between and 60%as much current"4 as the bottom rods and states that the upper tier onlyprojects down to the point where the mass still contains some tar.Presumably the upper rods will carry virtually no current. Manfredinialso directs that the rods shall be carefully cleaned (which means thatthey must be cooled) before being re-introduced into the mass.Heretofore it has been considered by those experimenting with theManfredini type of construction that it is necessary to use clean rodsThe heat of the mass keeps' klo 2 and to introduce them into thatportion of the mass which was still somewhat fluid in order to get agood bond between the rods and the mass which is aided by the shrinkageof the mass as the tars are volatilized.

The essential feature of Manfredini is that he uses enough contact rodsso that when a rod is withdrawn and reinserted, it does not have to godown into the conductive zone but is inserted only into the zone wherethe paste is soft. Here the paste gradually shrinks around the rod andwhen it has finally hardened, the electrode forms an integral andcontinuous mass directly contacting the rod. To do this it was of coursenecessary to use considerably more rods than the minimum numbernecessary to carry the necessary electrical current. In fact, abouttwice as many.

I have discovered that the number of rods can be greatly reduced andmuch more efcient results can be had by working on a different theory ofoperation.

The change in conductivity of the electrode mass does not vary uniformlyfrom the bottom to the top, and in order to get good conductivity, onemust go down in the electrode to a point where it is very hot. Thecritical temperature where goed conductivity is reached may vary undercertain circumstances, but in any event to get satisfactoryconductivity, one should go down in the mass to the point where thetemperature is at least 600 C. and preferably somewhat higher. At thistemperature the mass is incandescent and of course the mass at thistemperature is entirely solidified and baked hard.

In accordance with my invention when a rod is withdrawn, an amount ofunbaked paste is dropped into the hole insufficient to ll it above theline of incandescence, and then quickly before this paste can solidify,the rod is driven down into it. This does not give the paste a chancegradually to shrink about the rod as was formerly suggested, butapparently a substantial pressure is developed by forcing the rod intothe unbaked paste which is held by the fully hardcned electrode masssurrounding it. With this method of operation there are two successivecontact surfaces which may cause voltage drop and so might createdifllculties. One is the surface between the rod and the newly-hardenedpaste and the other is the surface between the solidified electrode massand the new paste which was added. Nevertheless, I have discovered thatactually the contact drop resulting from this operation is surprisinglylow and apparently is no greater than where the mass of paste is allowedslowly to shrink and harden about the rod as was formerly thoughtnecessary.

If the operator works rapidly following my procedure it is possible tohave a rod broken loose and reinserted and again carrying current in amatter of two or three minutes, which may be compared with the fact thatin the previously suggested operation a newly-inserted rod would not becarrying its full load of current until it had been in the mass forabout two weeks. In fact the change of rods takes so little time that Ionly need to supply the number of rods computed as necessary to supplythe current during regular operation.

It is. of course, important that the amount of fresh paste inserted inthe hole left by the withdrawn stud be carefully determined. This may bedone by pouring in a predetermined amount of pre-melted paste, or asausage-like plug of cold (and therefore solid) paste of proper size maybe dropped in the hole. If the cold solid plug is employed it will ofcourse melt quite quickly at the temperature of the bottom of the holeand will remain fluid for a reasonable length of time before it issolidified and carbonized. This latter procedure may reduce thenecessary speed of action by a minute or two but in any event no unduetime must be ailowed to elapse before the stud is driven back intoplace. For example, if as much as 25 minutes is allowed to elapsebetween the time that the extra paste is added and the time that thestud is returned to position, virtually no bond will be obtained soalmost no conductivity will result, In fact in such case it will bealmost impossible to drive the stud back down to the desired level. Thatwould mean that the hole would have to be illled with soft paste asunder the old method, and then wait for many days before it could carryits electrical load. I have found that careful cleaning of the rodsbefore re-insertion is not necessary.

Since the paste at the top of the mass is fluid when first added (thatis after it heats above its melting point) precautions have to be takento prevent an undue amount of paste from flowing down into the hole leftby the withdrawn stud. One way to take care of this is to withdraw thehot stud part way so that a heated portion of the stud is adjacent theuid paste. This can be left for a couple of hours to harden the pastearound the hole so that there will be no flow. It has also been foundthat if a group of studs are changed in a batch and a new paste is addedsoon after the studs are returned, enough heat will be conducted throughthe studs to solidify` the paste immediately around them to the pointwhere inflow will be virtually negligible. For example, if the paste isallowed to stand for as much as three days around the studs before theyare withdrawn, there is very little danger of the paste flowing into theopen hole and if the studs are withdrawn on a cycle of 6 or 7 days andnew paste is added shortly after the studs are reinserted, there is nodifficulty in this direction.

In the accompanying drawing I show a section through a continuousself-baking electrode of the type used for the production of aluminium,which is fitted with vertical contact rods which illustrate-the methodof my invention.

In these drawings, I designates the electrode mass. This is sectioned asa solid but it is understood that the upper part actually will beliquid. 'I'he broken line through the mass indicates approximately thetransition line where the mass is solidified. I2 indicates the fixedcasing in which the electrode mass moves. The 5 fixed casing issuspended by rods Il from transverse beams as indicated at i8.

Current is fed to the electrode mass Il by iron contact rods I B, eachof which has a hole I! for a pin. Four of these contact rods appear inthe transverse section and it is understood that additional numbers willbe in line with those indicated. For the purpose of explanation, thefour rods shown are marked respectively ila, IIb, llc and Id. Each ofthe rods Il is bolted to a support bar 20. These bars are clamped to thebus bars 22. The bus bars 22 can be raised Aand lowered by the jacks 2l.

When the lower end of a contact rod Il gets down too close to the bath(say within about to cm.) as in the case of rod Ila, such rod has to beraised and repositloned. To do this the rod is loosened from the bus bar22 and an appropriate tool as indicated at III is dropped over the endof the rod Il gripping the pin inserted into hole I9. The tool is thentwisted to loosen the rod I8 and the rod Il is withdrawn. A small amountof paste (by which term I mean the carbonaceous material of the typefrom which the electrode is formed, which is pasty when warm but whichin this case may be in the form of a cold, solid, sausage-like mass) isdropped into the hole left on the removal of the rod Il, but this amountof paste is insufficient to fill the hole above the incandescent level.Ordinarily it will be satisfactory if enough paste is put in the hole toraise the rod 20 or 40 cm. The rod Il is then quickly forced firmly downinto the hole, preferably while the rod is still incandescent. Thepaste, which has softened but is not yet baked, is squeezed up aroundthe rod between the sides of' the rod tip and the already solid, bakedelectrode mass and is immediately baked and hardened to grip the tip ofthe rod firmly and to form an almost integral mass with the I previouslysolidified electrode.

In the drawings, the rods IBb and ild are in the upper position and donot need to be changed. The rod |8c has just been changed and thenewly-inserted electrode mass is here cross-hatched I to show the spacewhich it is occupying, though actually it will be so merged with themain mass of the electrode that electrically it will form a continuouswhole. I'he rod llc will be so firmly anchored into place that it can beused almost Il immediately to carry its share of the weight of theelectrode and also to transmit electrical current to the electrode mass.

The tips of the rods I I are preferably tapered so as to leave spacewithin which the soft elec- N trode mass can be squeezed between therods and the fully baked electrode mass. These rods may, for example,have the following dimensions:

Millimeters u Diameter at the lower end Diameter at 300 mm. from thebottom 97 Diameter at '150 mm. from the bottom -100 It is understoodthat these figures are given only by way of illustration and to enableone to 7o build a device of this type to the best advantage. In theforegoing example I have shown the best method now known to me ofcarrying out my new method, but it is understood that the same may bemodified in many particulars without departing from the spirit of myinvention.

This application is a continuation in part of my earlier applicationSerial No. 587,513, filed April 10, 1945, which application has beenaber;u doned and replaced by the present application.

What I claim is:

1. In the operation of an electric furnace including a self-bakingcontinuous electrode having a bottom portion heated to a temperature inexcess of 750 C. and a top portion formed of soft unbaked paste andprovided with metal rods for suspending said electrode and for supplyingcunrent thereto, the method of re-positioning such rods when the wear ofthe bottom portion of the electrode makes it necessary to re-adjust suchmetal rods to a higher level which comprises: loosening a rod to bere-positioned and withdrawing it from the bottom of the hole, insertingin its hole an amount of unbaked carbonaceous paste material of a typewhich is molten when hot and adapted subsequently to harden by evolutionand decomposition of binder ingredients and in an amount sufficient tofill the botltom of the hole for an appreciable distance butinsufficient to prevent a rod from being re-inserted so that its tipwill extend below the top level of incandescense of the electrode andimmediately, before such paste can solidify and harden, forcing a rodfirmly down into the hole with its tip below the top level ofincandescence whereby soft paste is compressed between the rod and thesides of the hole and baked, and the rod is sealed in place and quicklybrought into good electrical conductivity with. the electrode mass.

2. A method as 'specified in claim 1 in which the amount of pastedropped in the hole has a volume equivalent to the capacity of the holefrom the bottom up to a point between 20 cm. and 40 cm. from the bottom.

3. A method as specified in claim 1 in which the rod has a tapered tipand is forced down into the hole with suiilcient force to squeeze meltedpaste up around the sides of the rod to seal the sides of the rod to thealready solid electrode mass.

4. A method as specied in claim l in which the rod is reinserted in theelectrode while it is still incandescent.

5. 1n the operation of an electric furnace in cluding a self-bakingcontinuous electrode pro-l vided with metal rods for suspending saidelec trode and supplying current thereto, the lower ends of all of theserods being normally located in the baked bottom portion of theelectrode, the method which comprises, when the wear of said bakedbottom portion makes it necessary to readjust the metal rods at a higherlevel with respect to the mass of the electrode, loosening and fullywithdrawing each of said rods from said electrode in two steps with atime interval between them, introducing a small amount of raw electrodepaste into the space thus left empty in the baked bottom portion of theelectrode, and driving back said rod into said space in said bakedportion down to a relative level slightly above the preceding one andextending down into the zone of incandescence so as to compress saidamount of raw paste between the rod and the electrode mass and thus toensure immediate baking thereof.

6. A method as specified in claim 1 in which each rod is given atwisting movement to loosen it in the electrode before it is withdrawn.

7. A method as specified in claim 1, in which the unbaked carbonaceouspaste material is added in a substantially solid form and allowed tomelt in the hole and in which the rod has a tapered tip and is forceddown into the hole with suicient force to squeeze melted paste up aroundthe sides of the rod to seal the sides of the rod to the already solidelectrode mass.

ROBERT JOUANNET.

REFERENCES CITED The following referenlces are o'f record in the ille ofthis patent:

UNITED STATES PATENTS Name Date Westly May 6, 1930 Trematore Nov. 30,1937 Sem May 23, 1939 Manfredini Dec. 10, 1946 FOREIGN PATENTS @THEIRREFERENCES Sem et al., `lourhal of the Electrochemical Society, volume9i, No. 5, November, 1948 (pages 1220-231).

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